A. Field of Invention
This invention pertains to the field of biomedical data processing. More specifically, this invention pertains to the field of body activity measurement using multiple activity/pressure detecting transducers, such as piezoelectrics.
B. Description of Prior Art
1. Problem Statement/Objects of Invention
Ideally, for a body activity monitor to be technically and economically suitable for extended periods of time and during all normal daily activities, it should be accurate, repeatable, easy to manufacture, simple in structure, inexpensive, easy to use, give continuous activity expenditure data, be comfortable to the patient, be low in power consumption, be small in size, have very few environmental restrictions on its usage, be easily applied to the patient, be easy to calibrate, be reliable, and measure activity as directly as possible (to maximize activity data correlation and minimize secondary effect correlations that cause errors with indirect methods).
2. Prior Art Performance
Most of the small in size, portable prior art appear to satisfy most of the requirements of the instant invention, except accuracy and repeatability. Much of this is due to the simple switch or accelerometer transducers being placed at the waist.
At first glance, putting the transducer in a box at the waist has three major advantages:
a. Major energy consuming activities have motions at the at the waist, so a waist-located sensor should indicate the general trend of the body's energy expenditure during motion.
b. The box should protect the sensor from being broken or from being taken out of calibration.
c. If only one sensor is used, only one sensor needs to be built and only one sensor channel needs to be calibrated.
The researchers who developed these devices have shown that these methods commonly underestimate energy expenditures for some major activities by as much as a factor of 3 and overestimate other activities by as much as a factor of 2.
These problems are fundamentally due to these methods not measuring the activity of the major activity generating parts of the body: the arms and legs. For example, if these devices are calibrated at a mid-speed walking activity, they overestimate jumping rope and running and underestimate toe touching, sit-ups, and leg lifts.
Documentation to support the above prior art description can be found in the following publications:
a. U.S. Pat. No. 4,192,000. (filed 1977, issued 1980). Cl. 364-415. Elmer M. Lipsey. Electronic Calorie Counter. This device uses a magnetic sensor at the waist to measure motion.
b. Other Sources.
Hemokinetic Inc. (2923 Osmundsen Rd., Madison, WI. 53711). This company produces a device called Caltrac which is the marketed version of Servais, Webster, and Montoye's device.
Servais, Webster, and Montoye. "Estimating Human Energy Expenditure Using an Accelerometer Device." J. of Clinical Engineering. April-June 1984. Uses a piezoelectric bender as an acceleration detecting sensor at the waist. Assumes (incorrectly) that body energy expenditure is linearly proportional to acceleration at the waist.
Wong, Webster, Montoye, and Washburn. "Portable Accelerometer Device for Measuring Human Energy Expenditure." IEEE Trans. Biomedical Engineering. June 1981. Precursor to the 1984 Servais, Webster, and Montoye device. Uses a waist worn modified ceramic phonocartridge as the transducing element.
3. This Invention's Performance
This invention is different and better than the prior art because it solves all of the problems listed earlier; especially accuracy and repeatability. It measures the work done by the major moving elements of the body. (energy=the change in work=force times distance). Pressure/force piezoelectric transducers measure the force and speed that the elements are experiencing and also the time that the elements are moving. (since energy=the force times distance=force times speed times time, we are measuring energy directly).